Pigment analysis of Portuguese portrait miniatures of 17th and 18th centuries by Raman Microscopy and SEM‐EDS

Abstract

Seventeen Portuguese miniature portraits on copper support from the Évora Museum collection (Portugal) were analyzed in situ and nondestructively by Raman microscopy (RM), SEM-EDS, and stereomicroscopy. This work constitutes a great breakthrough in the study of miniature paintings from the 17 th and 18 th centuries, since the chemical information known about this unique kind of paintings are still scarce, and in particular, this exclusive collection was never been subjected to any physicochemical study. In this work, each portrait was examined in detail in order to characterize the pigments palette used by the miniaturists. The μ-Raman analysis, in particular, guaranteed an exceptional visualization and good individual identification of small grains of pigments and other constituents of the pictorial layer. Using this technique, 19 compounds were identified, including bluish black covellite, a pigment rarely found in oil paintings. SEM-EDS was used as an important complementary technique to confirm the chemical nature of some pigments and to identify shell gold (gold dust) in some portraits. Overall, the pigments identified in this large set of old paintings are broadly consistent with those mentioned in the painting treatises of that time or reported in other more modern bibliographic sources.

Micro-analytical study of two 17th century gilded miniature portraits on copper

“…The reliability of some of these techniques in the chemical analysis of miniature portraits on copper plate were in fact recently demonstrated [10]. The only exception to the non-invasive and non-destructive approach, involved the collection of a single microsample from one painting, and its analysis by LC-DAD-MS to discover the molecular identity of a dark red pigment.…”

“…In order to know the molecular composition of the pigments, which appear in the form of grains of micrometric dimensions in a quite complex matrix, it was implemented a systematic analysis point-by-point (taking advantage of a spatial resolution > 1 m). Despite the strong background fluorescence for most paintings, no treatment of baseline adjustment or smoothing was performed, because there is no substantial gain [10].…”

“…The analysis of the miniature paintings were performed by variable pressure scanning electron microscopy (Hitachi S3700N) coupled with energy dispersive X-ray spectrometry (BRUKER Xflash 5010SDD), without any sampling or preparation of the artworks as described elsewhere [10]. In short, both miniatures were inserted in the specimen chamber of the scanning electron microscope.…”

“…As described elsewhere [10], the pigments analysis was performed by Raman microspectrometry, using a HORIBA Xplora Raman microscope, with capacity A C C E P T E D M A N U S C R I P T…”

Analytical study of the XIV century wall painting and lime mortars in the "St. George" church in Staro Nagoričane, Republic of Macedonia

“…6b) suggested the presence of apatite-based minerals (Ca-phosphates group) [16,[20][21][22]. According to the relevant literature [20,[23][24][25], the inorganic component hydroxyapatite (Hap) (Ca 5 (PO 4 ) 3 (OH)) or carbonate-Hap (Ca 5 (PO 4 ,CO 3 ) 3 (OH)) is commonly present in the carbon-based black pigments of animal origin. Hence, the detection of phosphorous and phosphate group was accepted as a reasonable indicator of the presence of bone or ivory black pigments.…”